A Brisbane mother will run in one of the most challenging marathons in the world this weekend in memory of her first-born son who was stillborn at 37 weeks.

Anita Marshall is set to compete in the world-famous New York Marathon for her son Charlie who would have turned 13 this year.

Ms Marshall, who has never run a marathon before, decided to run to honour her son's memory, as well as raise awareness and funds for not-for-profit organisation Miscarriage, Stillbirth and Newborn Death Support (Sands).